Internally-shielded microelectronic packages and methods for the fabrication thereof

ABSTRACT

Internally-shielded microelectronic packages having increased resistances to electromagnetic cross-coupling are disclosed, as are methods for fabricating such microelectronic packages. In embodiments, the internally-shielded microelectronic package includes a substrate having a frontside and a longitudinal axis. A first microelectronic device is mounted to the frontside of the substrate, while a second microelectronic device is further mounted to the frontside of the substrate and spaced from the first microelectronic device along the longitudinal axis. An internal shield structure includes or consists of a shield wall, which is positioned between the first and second microelectronic devices as taken along the longitudinal axis. The internal shield structure is at least partially composed of a magnetically-permeable material, which decreases electromagnetic cross-coupling between the first and second microelectronic devices during operation of the internally-shielded microelectronic package.

TECHNICAL FIELD

Embodiments of the present invention relate generally tomicroelectronics and, more particularly, to internally-shieldedmicroelectronic packages and methods for the production thereof.

ABBREVIATIONS

Abbreviations appearing relatively infrequently in this document aredefined upon initial usage, while abbreviations appearing morefrequently in this document are defined below:

ACM—air cavity molded or molded air cavity;

Cu—copper;

EM—electromagnetic;

PA—power amplifier;

PCB—printed circuit board; and

RF—radio frequency.

BACKGROUND

EM cross-coupling (more informally, “cross-talk”) can occur betweenseparate signal paths within circuitry integrated into or housed withinmicroelectronic packages. EM cross-coupling may be particularlyproblematic in the context of small scale, high power RF applications.Consider, for example, an RF microelectronic package containing N-wayDoherty PA circuitry and having a relatively compact form factor. Bycommon design, such a microelectronic package may contain two or morehigh gain transistor die attached to a base flange in a side-by-siderelationship. Bondwire arrays may electrically interconnect thetransistor die with other circuit elements, such as the packageterminals, integrated passive capacitors, or other devices containedwithin the package. Due to the close proximity of the transistor die andtheir corresponding bondwire arrays, EM cross-coupling can occur duringpackage operation and, if sufficiently severe, may limit the performanceof the RF PA circuitry; e.g., EM cross-coupling may displace impedancespresented to the transistor die, which may detract from RF performancein terms of linearity, efficiency, peak power, or gain. Similarly, EMcross-coupling can likewise limit the performance of microelectronicdevices containing other types of circuitry, which include signal pathsextending in relatively close proximity and carrying distinct electricalsignals.

There thus exists an ongoing demand for the provision of microelectronicpackages having reduced susceptibility to EM cross-coupling, even whencontaining (e.g., RF) circuitry operated at higher power levels andpossessing relatively compact form factors. Ideally, embodiments of suchmicroelectronic assemblies would provide enhanced shielding of adjacentsignal paths from EM cross-coupling, while maintaining high levels ofpackage performance and remaining cost effective to manufacture.Similarly, it is desirable to provide methods for manufacturingmicroelectronic packages having such favorable characteristics. Otherdesirable features and characteristics of embodiments of the presentdisclosure will become apparent from the subsequent Detailed Descriptionand the appended Claims, taken in conjunction with the accompanyingdrawings and the foregoing Background.

BRIEF DESCRIPTION OF THE DRAWINGS

At least one example of the present invention will hereinafter bedescribed in conjunction with the following figures, wherein likenumerals denote like elements, and:

FIGS. 1 and 2 are upper and lower isometric views of aninternally-shielded ACM package, respectively, which includes aleadframe-integrated shield structure and which is illustrated inaccordance with an exemplary embodiment of the present disclosure;

FIG. 3 is an isometric view of the internally-shielded ACM package shownin FIGS. 1-2, as illustrated with the cover piece removed to reveal theinternal shield structure and other features contained within theexemplary package;

FIGS. 4-7 illustrate the internally-shielded ACM package shown in FIGS.1-3, as depicted at various stages of manufacture and fabricated in anaccordance an exemplary ACM package fabrication process;

FIG. 8 is an isometric view of a second exemplary internally-shieldedACM package, which includes a discretely-fabricated shield insert pieceor “inserted shield structure” and which is illustrated at anintermediate stage of manufacture;

FIG. 9 is a detailed view illustrating one manner in which the insertedshield structure can be attached to the leadframe of the exemplary ACMpackage shown in FIG. 8 in embodiments;

FIG. 10 is a partially exploded view of an internally-shielded ACMpackage including an internal shield structure attached to or integrallyformed with underside of a cover piece, as illustrated in accordancewith a still further exemplary embodiment of the present disclosure; and

FIG. 11 is a lower isometric view of the cover piece contained theexemplary ACM package shown in FIG. 10 more clearly illustrating onemanner in which the internal shield structure can be integrally formedwith or otherwise joined to the cover piece.

For simplicity and clarity of illustration, descriptions and details ofwell-known features and techniques may be omitted to avoid unnecessarilyobscuring the exemplary and non-limiting embodiments of the inventiondescribed in the subsequent Detailed Description. It should further beunderstood that features or elements appearing in the accompanyingfigures are not necessarily drawn to scale unless otherwise stated. Forexample, the dimensions of certain elements or regions in the figuresmay be exaggerated relative to other elements or regions to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. The term “exemplary,” as appearing throughout this document,is synonymous with the term “example” and is utilized repeatedly belowto emphasize that the following description provides only multiplenon-limiting examples of the invention and should not be construed torestrict the scope of the invention, as set-out in the Claims, in anyrespect.

The term “air cavity package,” as appearing throughout this document,refer to a microelectronic package including a sealed cavity at leastpartially filled with a gas, regardless of the internal pressure withinthe cavity. The “air cavity” of the air cavity package may be enclosedin an open air environment and, thus, may contain air at approximately 1atmosphere pressure with slight variations depending upon elevation andprocessing temperatures during package manufacture. In otherimplementations, the “air cavity” of the air cavity package may beenclosed in a partially evacuated chamber or a chamber containing aninert gas, such as argon, during manufacture and, thus, may not containpure air in all instances. The term “air cavity,” then, should beunderstood as referring to a gas-containing cavity, which may or may notbe partially evacuated and which is sealed from the ambient environment.The seal formed between the air cavity and the ambient environment maynot be hermetic, as strictly defined, but rather may be a low leakageseal having a gross leakage rate falling within acceptable parameters.Thus, as appearing herein, a cavity is considered “sealed” when littleto no leakage (bubbles) are observed from the cavity's exterior when thecavity is filled with air or another gas and the air cavity package isfully immersed in a liquid (e.g., Perfluoropolyether (PFPE)) atapproximately 125 degrees Celsius (° C.). Finally, the term “molded aircavity package” and the corresponding term “ACM package” refer to an aircavity package, as previously defined, and further including a packagebody principally or exclusively formed from one or more moldedmaterials.

DEFINITIONS

The following definitions apply throughout this document. Those termsnot expressly defined here or elsewhere in this document are assignedtheir ordinary meaning in the relevant technical field.

Electrically-conductive material—A material having an electricalresistivity less than 1 milli-Ohm millimeter at 2020 C.

Internal shield structure—A structure including or consisting of acentral shield wall contained within a microelectronic package anddecreasing the electromagnetic cross-coupling between different signalpaths in at least some instances of package operation.

Magnetically-permeable material—A material having a relative magneticpermeability (μ_(r)) exceeding 1000.

Mu metal—any alloy principally composed of nickel (Ni) and iron (Fe), byweight, and having a relative magnetic permeability (μ_(r)) exceeding10,000.

Relative magnetic permeability (μ_(r))—the ratio of magneticpermeability of a material or medium (μ) over the magnetic permeabilityof free space (μ₀).

Supermalloy—an alloy predominately composed of Ni, Fe, and molybdenum(Mo), by weight, and having a relative magnetic permeability exceeding10,000.

OVERVIEW

Internally-shielded microelectronic packages having increasedresistances to EM cross-coupling are disclosed, as are methods forfabricating such microelectronic packages. Embodiments of themicroelectronic package contain unique internal shield structures, whichprovide enhanced shielding between adjacent circuit elements (e.g.,interconnect features or microelectronic devices) contained within thepackages and carrying distinct electrical signals during packageoperation. The internal shield structure can provide enhanced shieldingprincipally from a magnetic perspective, from an electrical perspective,or both, depending upon the particular construction and composition ofthe shield structure. In various embodiments, the internal shieldstructure is at least partially composed of a body or layer ofmagnetically-permeable material, which is positioned and dimensioned toreduce magnetic cross-coupling between adjacent interconnect features ormicroelectronic devices located within the microelectronic package.Additionally or alternatively, the internal shield structure may be atleast partially composed of an electrically-conductive material tofurther reduce electric cross-coupling between parallel signal paths oradjacent microelectronic devices. In this latter case, the internalshield structure (or at least the electrically-conductive portionthereof) may be electrically grounded to, for example, reduce eddycurrent losses and provide other performance benefits. Generally, then,embodiments of the internal shield structure may enhance packageperformance by reducing or eliminating EM cross-coupling, which mayotherwise occur absent the provision of the internal shield structure.

The internal shield structure may possess different dispositions withina given microelectronic package, noting that a single package maycontain two or more shield structures in certain instances. In someimplementations, the internal shield structure may include a main bodyhaving wall-like or plate-like form factor (herein, “a shield wall”),which partitions adjacent microelectronic devices (e.g., semiconductordie) attached to a flange or other substrate contained in themicroelectronic package. The shield wall may be oriented to extendsubstantially orthogonal to the frontside of a flange and, perhaps, maybe imparted with a height equal to or greater than the height or heightsof the microelectronic device(s) mounted to the flange. In certaincases, when the microelectronic package is fabricated utilizing aleadframe-based manufacturing approach, the internal shield structuremay be integrally formed with the leadframe for increased manufacturingefficiency. For example, in such cases, the shield wall may be providedas a flat rectangular or blade-like section of the leadframe, which isbent upwardly or “flipped up” into an upright or deployed positionduring package manufacture. In other embodiments, the internal shieldstructure can be provided as discretely-fabricated piece or insert,which is joined to the package infrastructure, such as the leadframe orbase flange, during package manufacture. In still other embodiments inwhich the package contains an air cavity, the internal shield structurecan be integrally formed with or joined to the underside of a coverpiece utilized to enclose the air cavity. All of the aforementionedembodiments can be combined, as well, to yield still furtherpermutations of the present disclosure.

Embodiments of the internally-shielded microelectronic package caninclude various other features in addition to or in lieu of thoseset-forth above. For example, in some implementations, the internalshield structure may be fabricated to include one or more (often two)lateral extensions, which project outwardly from the package body andextend between neighboring sets of package leads to provide supplementalEM shielding at this location. When included within the microelectronicpackage, such lateral extensions may also extend onto and over asubstrate, such as a PCB, to which the package is mounted; e.g., tofurther provide shielding between traces or other electrical routingfeatures on the PCB. The lateral extensions may also facilitateelectrical grounding of the internal shield structure. Additionally oralternatively, in instances in which the microelectronic packageincludes a base flange or other electrically-conductive substrateserving as a package terminal, the internal shield structure may beelectrically coupled to the base flange by physical contact, through anelectrically-conducive bonding material provided at a juncture betweenthe shield structure and flange, or both. Such an approach may be usefulwhen the internal shield structure contains an electrically-conductiveportion or layer, which is desirably coupled to electrical groundthrough the base flange. In still other implementations, the internalshield structure may not be electrically grounded or may be electricallygrounded in a different manner; e.g., by providing the microelectronicpackage with a dedicated lead extending from the shield structure to theexterior of the package for grounding purposes. Exemplary embodiments ofinternally-shield microelectronic packages and methods for fabricatingsuch packages will now be described in conjunction with FIGS. 1-11.

Non-Limiting Example of an Internally-Shielded Microelectronic Package

FIGS. 1-3 illustrate a microelectronic package 20 in accordance with anexemplary embodiment of the present disclosure. Microelectronic package20 assumes the form of a leaded ACM package in the illustrated exampleand will consequently be referred to hereafter as “ACM package 20.” ACMpackage 20 includes a number of package leads 22, 24, 26, 28, 30, 32,which project from a molded package body 34 for interconnection whenpackage 20 is installed within a microelectronic module, system, or thelike. In alternative embodiments, microelectronic package 20 may containa different number and type of leads or may instead assume the form of ano-lead package. Molded package body 34 includes a peripheral sidewall,which defines or bounding the outer perimeter of an air cavity 36 (FIG.3) located within package 20. Air cavity 36 is enclosed by a lid orcover piece 38 (FIGS. 1-2) positioned over and attached to moldedpackage body 34; e.g., cover piece 38 may be sealingly bonded to theupper peripheral edge of package body 34 utilizing a bead of adhesive.Cover piece 38 is removed in FIG. 3 to reveal the interior of moldedpackage body 34, air cavity 36, and a number of microelectronic devices44, 46 contained in air cavity 36, as discussed more fully below. Moldedpackage body 34 is formed in contact with and extends around orpartially envelopes a substrate or base flange 40. As shown in FIG. 2,the lower principal surface or backside of base flange 40 may be exposedthrough a lower surface of molded package body 34 to facilitateelectrical connection and/or efficient thermal contact with anotherbody, chassis, or substrate on which package 20 may be installed.

As can be seen in FIG. 3, microelectronic devices 44, 46 are mounted toan upper principal surface or frontside 42 of base flange 40.Specifically, in the illustrated example, two microelectronic devices44, 46 are located within air cavity 36 and bonded or otherwise attachedto frontside 42 of base flange 40 in a side-by-side relationship.Microelectronic devices 44, 46 are spaced along a longitudinal axis ofACM package 20, which is represented by double-headed arrow 45 in FIGS.1-2 and which extends parallel to package centerline 52. Microelectronicdevices 44, 46 can be, for example, semiconductor die bearing integrated(e.g., RF) circuity and having a number of bond pads 48 thereon. Inother embodiments, ACM package 20 can contain a different number andtype of microelectronic devices including various combinations ofintegrated passive devices, discretely-placed passive devices (e.g.,capacitors, inductors, resistors, or diodes in the form of Surface MountDevices (SMDS)), Microelectromechanical systems (MEMS) devices,semiconductor die, RF antenna structures, and optical devices, to listbut a few examples.

When enclosed by bonding cover piece 38 (FIGS. 1-2) to molded packagebody 34, air cavity 36 may contain air, another inert gas (e.g.,nitrogen), or a gas mixture. Air cavity 36 may or may not be partiallyevacuated or pressurized relative to the ambient environment, with thegaseous contents and pressure of air cavity 36 largely determined by theenvironment and temperature conditions during cover piece attachment.The hermicity of air cavity 36 will vary amongst embodiments, althoughACM package 20 is usefully produced such that relatively little, if anyleakage occurs between cavity 36 and the ambient environment when coverpiece 38 (FIGS. 1-2) is installed over and bonded to molded package body34. In other embodiments, microelectronic package 20 may lack moldedpackage body 34, in which case air cavity 36 may be peripherally boundedby one or more non-molded structures, such as a dielectric window frame.Alternatively, in further implementations, molded package body 34 may beformed as a solid mass of material or block of encapsulant followingdevice attachment and interconnection, in which case package 20 may lackair cavity 36 altogether.

Base flange 40 can be any body of material, layered structure, orcomposite structure serving as a substrate or carrier supporting themicroelectronic devices (i.e., devices 44, 46) located within air cavity36. Accordingly, base flange 40 may assume the form of a metallic plate,slug, or other monolithic body in certain implementations. In otherembodiments, base flange 40 can be fabricated from organic materials(e.g., a resin similar or identical to that from which printed circuitboards are produced) containing metal (e.g., Cu) coining. In stillfurther instances, base flange 40 may have a multilayer metallicconstruction; e.g., base flange 40 may contain multiplethermally-conductive layers, which are bonded in a laminatedarrangement. In many cases, base flange 40 will be predominatelycomposed of one or more metals having relatively high thermalconductivies, such as Cu. As a specific example, in an embodiment inwhich base flange 40 is a layered or laminated structure, base flange 40may include at least one Cu layer combined with at least one disparatemetal layer having a coefficient of thermal expansion (CTE) less thanthat of the Cu layer. The disparate metal layer may be composed of, forexample, Mo, a Mo—Cu alloy, or a Mo—Cu composite material. In thismanner, base flange 40 may be imparted with both a relatively highthermal conductivity and a lower effective CTE, which is more closelymatched to that of microelectronic devices 44, 46 and/or to that ofmolded package body 34. Base flange 40 may serve as anelectrically-conductive terminal of ACM package 20, as a heatsink orheat spreader, or both in embodiments of package 20.

The inner terminal end portions of package leads 22, 24, 26, 28, 30, 32extend into the package interior for connection to microelectronicdevices 44, 46 contained within package 20. The inner terminal endportions of package leads 22, 24, 26, 28, 30, 32 are identified in FIG.3 by reference numerals “50” and are referred to hereafter as the“proximal” lead portions; the term “proximal,” and the antonym “distal,”defined based upon relative proximity to the package interior and aircavity 36 (when present). Proximal lead portions 50 are exposed withinthe package interior along an inner peripheral ledge or bond pad shelf54 of molded package body 34. In the illustrated example, proximal leadportions 50 are interconnected to corresponding bond pads 48 on devices44, 46 utilizing a number of bondwires 56 to complete the desired wiringstructure. For example, in one implementation, leads 22, 24 project froma first side of ACM package 20 and serve as input leads electricallycoupled to the input (e.g., gate) terminals of microelectronic devices44, 46; while leads 26, 28, 30, 30 project from a second, opposing sideof package 20 and serve as output leads electrically coupled to theoutput (e.g., drain) terminal of devices 44, 46. In certain instances,base flange 40 may itself serve as a ground reference terminal of ACMpackage 20 and, therefore, may be electrically coupled to a sourceterminal of devices 44, 46. In other embodiments, different wiringarchitectures and other types of interconnect features (e.g., threedimensionally printed traces) may be employed.

ACM package 20 further contains an internal shield structure 58, whichis at least partially and, perhaps, entirely contained within air cavity36. As a point of emphasis, the particular form, disposition,composition, shape, and dimensions of internal shield structure 58 willvary among embodiments, as appropriate to suit a particular applicationor usage, providing shield structure 58 reduces EM cross-couplingbetween different signal paths during package operation. In manyinstances, and as indicated in FIG. 3, internal shield structure 58 willinclude a main body 60, which has a fin-like for plate-like form factorand which is referred to hereafter as “shield wall 60.” Generally,shield wall 60 may be positioned within package 20 at a location betweenadjacent microelectronic devices, interconnect features, and/or othercircuit elements, which carry disparate electrical signals and generateEM fields prone to interference during package operation absent theprovision of internal shield structure 58. Accordingly, and as indicatedin FIG. 3, shield wall 60 of internal shield structure 58 may bepositioned between microelectronic devices 44, 46, as taken alonglongitudinal axis 45 (FIGS. 1-2), such that opposing principal surfacesof shield wall 60 may face devices 44, 46. Further, internal shield wall60 may be oriented to extend orthogonally relative to base flange 40such that the opposing principal surfaces of shield wall 60 formessentially right angles with flange frontside 42.

The dimensions and shape of main shield wall 60 will vary amongstembodiments. Generally, it may be desirable to maximize the height ofshield wall 60, to the extent permitted by the dimensions of ACM package20, to accommodate the reach of the core EM fields induced when package20 is energized; the term “core EM fields,” as appearing herein,referring to those portions of the induced EM fields of sufficientmagnitude to warrant concern with respect to EM cross-coupling.Concurrently, manufacturing efficiency may be boosted by providinginternal shield structure 58 as an integral part of a leadframe when aleadframe-based manufacturing approach is utilized to fabricatedmicroelectronic package 20. One manner in which the height of shieldwall 60 may be maximized, while allowing wall 60 and, more broadly,internal shield structure 58 to be produced as an integral part of aleadframe, is as follows. Internal shield structure 58 may be initiallyproduced with shield wall 60 in a horizontally-oriented, non-deployedorientation, and shield wall 60 may be subsequently rotated into adeployed (vertically-oriented or upright) orientation following initialleadframe fabrication. In such embodiments, internal shield structure 58may be further imparted with flexure portions 62 (hereafter, “flexures62”) having a serpentine form factor, which ease bending stresses whenrotating shield wall 60 into the deployed orientation. As shown in FIG.3, flexures 62 may be coupled opposing ends of shield wall 60 andopposing anchor regions 64, which are further included in structure 58and which extend into molded package body 34 following thebelow-described overmolding process. Further description of the mannerin which shield wall 60 may be initially produced in a non-deployedorientation and subsequently rotated or “flipped-up” into an upright,deployed orientation is provided below in conjunction with FIG. 5.

When provided as a part of a leadframe, internal shield structure 58 maybe at least partially composed of the same material as are package leads22, 24, 26, 28, 30, 32. For example, in this case, internal shieldstructure 58 and package leads 22, 24, 26, 28, 30, 32 may be provided aspieces of a leadframe composed of a first electrically-conductivematerial, such as metal or alloy containing Cu, Ni, aluminum (Al),silver (Ag), gold (Au), or a combination thereof as primaryconstituents, by weight. The leadframe, or at least a portion of theleadframe encompassing shield wall 60 of internal shield structure 58may further be coated or covered with a second material, which has ahigher magnetic permeability and a lower electrical conductivity thandoes the first electrically-conductive material. This second material isrepresented in FIG. 3 by dot stippling and may be applied by plating,sputter deposition, or utilizing another deposition process, dependingupon the composition of the magnetically-permeable manner. Such aconstructions allows internal shield structure 58 to provide enhancedshielding of both electrical and magnetic aspects of EM cross-coupling.In other embodiments, the leadframe from which internal shield structure58 and package leads 22, 24, 26, 28, 30, 32 are formed may be composedof a magnetically-permeable metal, such as Mu metal, an iron-rich alloy(e.g., supermalloy), or an electrical steel, which is further platedwith an electrically-conductive alloy in those regions in whichelectrical conduction is desired; e.g., the upper surfaces of leads 22,24, 26, 28, 30, 32 including inner peripheral lead portions 50.

In embodiments in which internal shield structure 58 includes anelectrically-conductive portion or layer in addition to amagnetically-permeable portion or layer, it may be desirable to coupleshield structure 58 to electrical ground. In certain embodiments, thiscan be accomplished by providing an additional lead extending frominternal shield structure 58 to the exterior of ACM package 20 forgrounding purposes. More conveniently, however, internal shieldstructure 58 may be electrically coupled to base flange 40 when servingas a ground reference terminal of ACM package 20. In such embodiments,internal shield structure 58 may simply be placed in physical contactwith base flange 40 to form the desired electrical connection. A morereliable connection can typically be formed, however, via the provisionof an electrically-conductive body or layer of material provided at thejuncture between the lower edge of shield wall 60 and flange frontside42. To this end, shield wall 60 may be electrically coupled to flangefrontside 42 through a body of an electrically-conductive material 66,such as a metal-filled epoxy, a sintered metallic material, or otherelectrically-conductive adhesive. Grounding of shield wall 60 ofinternal shield structure 58 in this manner may reduce eddy currentloses, decrease RF mismatch issues (when applicable), lessen memoryeffects (hysteresis), and provide other benefits. This notwithstanding,internal shield structure 58 may not be electrically coupled to baseflange 40 or to electrical ground in further embodiments.

Advantageously, EM cross-coupling that may otherwise occur withinpackage 20, particularly when operated at higher power levels and havinga relatively small form factor, is reduced or eliminated via theprovision of internal shield structure 58. The enhanced resistivity toEM cross-coupling afforded by internal shield structure 58 may beespecially beneficial when, for example, package 20 contains an N-way(e.g., dual path) Doherty PA circuitry. In such embodiments,microelectronic devices 44, 46 may be high gain transistor die, such aslaterally-diffused metal-oxide-semiconductor (LDMOS), gallium nitride(GaN), or gallium arsenide (GaAs) transistors. In such embodiments,internal shield structure 58 may reduce EM cross-coupling between suchdie (devices 44, 46) and bondwire arrays 56 to prevent displacement ofthe impedances delivered to the die to maintain the linearity of thepeaking and carrier signal paths within package 20. This examplenotwithstanding, microelectronic package 20 can contain other types ofmicroelectronic devices and is not limited to any particular applicationor function. Further, in alternative embodiments, microelectronicpackage 20 can contain multiple shield structures similar or identicalto internal shield structure 58 and distributed within air cavity 36;e.g., package 20 can contain three or more microelectronic devices witheach neighboring pair of devices separated by a shield structure infurther implementations. Finally, while having a leadframe-basedconstruction in the illustrated example and in the exemplarymanufacturing process discussed below in conjunction with FIGS. 4-7,microelectronic package 20 need not contain a leadframe in allembodiments.

In embodiments, internal shield structure 50 may be fabricated tofurther include certain features or projections, which extend from thepackage interior to the package exterior. Examples of such features(hereafter, “shield extensions 81”) are shown in FIG. 3. Shieldextensions 81 may be omitted in versions of ACM package 20 and areconsequently illustrated in phantom (dashed line). When provided, shieldextensions 81 may project away from main shield wall 60 to the exteriorof package body 34 to, for example, provide enhanced EM isolationbetween adjacent sets of leads 22, 24 and 28, 30. In this regard, shieldextensions 81 may extend from opposing sides of shield wall 60 to thepackage exterior, with extensions 81 joined to shield wall 60 throughflexures 62 and anchor regions 64 as shown. Further, should ACM package20 be mounted to a PCB or other substrate having electrically-conductiverouting features thereon, shield extensions 81 may extend over and ontothe upper surface of the PCB to provide shielding between adjacent metaltraces (or other routing features) and/or to facilitate electricallygrounding of shield wall 60 and internal shield structure 58, generally.This possibility is further indicated in FIG. 3, which depicts twolimited regions 83 of a PCB over which extensions 81 may extend when ACMpackage 20 is installed on the PCB. The particular dimensions ofextensions 81, when included in package 20, will vary amongimplementations; however, in certain embodiments, extensions 81 mayextend from package body 34 beyond leads 22, 24, 28, 30. In furtherembodiments, internal shield structure 58 only include a single shieldextension 81 or may lack extensions 81 altogether.

Examples of Air Cavity Package Fabrication Methods

Whether produced on an individual basis or in parallel with a number ofother ACM packages, ACM package 20 is conveniently fabricated utilizinga leadframe-based manufacturing approach. In this regard, ACM package 20may be manufactured to incorporate a leadframe, which contains packageleads 22, 24, 26, 28, 30, 32 and other physically-interconnectedfeatures, at least some of which may be removed during the course of ACMpackage fabrication. An example of a leadframe 68 suitable for usage inthe manufacture of ACM package 20 is shown in FIG. 4. In this example,leadframe 68 is fabricated as a relatively thin strip or plate-like bodycomposed of a metallic material, such as Cu or a Cu-based alloy. Ifdesired, ACM package 20 may be fabricated as a discrete unit byindividually processing leadframe 68 as a pre-singulated structure.Process efficiency will typically be increased and manufacturing costslowered, however, by manufacturing ACM package 20 in parallel with arelatively large number of similar ACM packages. In this regard, ACMpackage 20 may be produced in parallel with other, non-illustrated ACMpackages by concurrently processing a plurality of leadframesinterconnected as a leadframe array. Such a leadframe array can containrelatively large number of leadframes arranged in, for example, a twodimensional grid layout or a linear strip layout.

The body of leadframe 68 is machined (e.g., stamped), etched, laser cut,or otherwise processed to define the various leadframe features. Inaddition to package leads 22, 24, 26, 28, 30, 32, these features includeinternal shield structure 58, central openings 70 on opposing sides ofstructure 58, and a number of connective fingers or spars (herein, “dambars 72”), only a few of which are labeled. Dam bars 72 join packageleads 22, 24, 26, 28, 30, 32 and internal shield structure 58 to theplate-like body of leadframe 68. Additionally, dam bars 72 mayfacilitate handing and positioning of leadframe 68 leading into and,perhaps, through the molding process. After molding, dam bars 72 may besevered and removed along with other sacrificial leadframe portions,such as outer peripheral leadframe portion 74. Regions 81 of leadframe68 may likewise be trimmed away or removed in embodiments; or, instead,one or both of regions 81 of leadframe 68 may be left intact to formshield extensions 81 described above in conjunction with FIG. 3. Outerperipheral leadframe portion 74 may include various openings or cutoutsfacilitating handling of leadframe 68 during ACM package fabrication.

At the stage of manufacture shown in FIG. 4, main shield wall 60 ofinternal shield structure 58 resides in an initial vertically-extending,non-deployed orientation. At a subsequent stage of manufacture, and asindicated by arrow 76 in FIG. 5, shield wall 60 is rotated into anupright, deployed orientation. As noted above, flexures 62 of internalshield structure 58 bend or deform to accommodate angular rotation ofshield wall 60 in this manner. The particular juncture at which shieldwall 60 is rotated into its deployed position can vary amongembodiments, but will typically occur prior to overmolding and theformation of package body 34, as discussed below in connection with FIG.6. As noted briefly before, forming internal shield structure 58 in thismanner enables the height of shield wall 60 to be maximized, whilefurther allowing structure 58 to be formed as an integral part ofleadframe 68. The height of shield wall 60 is measured along an axisparallel to package centerline 52 (FIGS. 1-2) and is identified in FIG.5 by double-headed arrow H₁. In embodiments, H₁ may be dimensioned to beequivalent to or greater than the height of devices 44, 46, as takenalong axes parallel to centerline 52 (FIGS. 1-2) and orthogonal toflange frontside 42. Shield wall 60 is also imparted with a maximumwidth, as identified by double-headed arrow W₁. The width (W₁) of mainshield wall 60 is further usefully maximized and, in embodiments, may beat least one half the width of openings 70, as measured between theinner end portions of leads 22, 28 and leads 24, 30 (further identifiedin FIG. 5 by double-headed arrow W₂). Similarly, the shield width W₁ maybe at one half the distance between opposing edges of bond pad shelf 54,shown in FIG. 4.

After rotation of shield wall 60 into its deployed or uprightorientation, base flange 40 is next positioned adjacent leadframe 68utilizing, for example, a pick-and-place tool. Base flange 40 can bepositioned with respect to leadframe 68 by movement of flange 40, bymovement of leadframe 68, or a combination thereof. As a specificexample, and referring to the exemplary orientation of base flange 40and leadframe 68 shown in the drawing figures, base flange 40 may beplaced on a temporary support structure, carrier, or fixture; andleadframe 68 may be lowered onto flange 40 to achieve the desiredpositioning. Such an approach may be useful when a plurality of ACMpackages are manufactured in parallel. In this case, an appropriatenumber of base flanges can be distributed across such a carrier orfixture, and a leadframe array may then be lowered into its desiredposition to concurrently position the interconnected leadframes relativeto the array of base flanges. Alternatively, the illustrated orientationof base flange 40 and leadframe 68 may be inverted, and base flange 40may be lowered onto leadframe 68 during flange-leadframe positioning.Base flange 40 may further be secured to leadframe 68 in some manner,such as by staking, spot welding, bonding, or the like; however, this isnot necessary in all embodiments.

Advancing to FIG. 6, overmolding is next conducted to create moldedpackage body 34, which envelopes selected regions of leadframe 68, baseflange 40, and anchor regions 64 of internal shield structure 58. Moldedpackage body 34 is produced to include an open upper end such that aircavity 36, not yet enclosed by cover piece 38, opens in an upwarddirection away from base flange 40. Molded package body 34 is formed toleave exposed the device mount areas of base flange 40 and proximal leadend portions 50 of package leads 22, 24, 26, 28, 30, 32. At somejuncture following the molding process, selected portions of leadframe68 may be severed or trimmed away including, for example, dam bars 72and outer peripheral leadframe portion 74. Leadframe singulation ortrimming therefore results electrical isolation of package leads 22, 24,26, 28, 30, 32 and internal shield structure 58, which may otherwise beelectrically bridged to base flange 40 by dam bars 72. A non-exhaustivelist of processes suitable for singulating or trimming leadframe 68include sawing, laser cutting, water jetting, stamping, scribing (withor without punching), and routing.

Microelectronic devices 44, 46 may now be installed within ACM package20 by mounting or attachment to frontside 42 of base flange 40, as shownin FIG. 7. Device attachment can be performed utilizing any adhesive orbonding material including organic pressure-sensitive adhesives, suchcommercially-available die attach materials. Alternatively, deviceattachment may be conducted utilizing a metallic-based bonding process,such as a low temperature sintering process. Following deviceattachment, appropriate electrical interconnections are formed betweenthe installed microelectronic device(s) and the terminals exposed fromwithin the package interior. In the case of exemplary package 20,specifically, ball bonding or another wirebonding process isconveniently performed to form bondwires 56 electrically coupling bondpads 48 of microelectronic devices 44, 46 to the exposed upper surfacesof proximal end portions 50 of package leads 22, 24, 26, 28, 30, 32, asshown in FIG. 3. In other embodiments, a different interconnectiontechnique can be utilized. Electrical testing may further be performed,if desired, following device attachment and prior to the below-describedcover piece attachment operation.

To complete the package fabrication process and yield the completedversion of microelectronic package 20 shown in FIGS. 1-3, cover piece 38is attached to the upper peripheral edge portion of molded package body34. In certain instances, a low temperature sintering process can beutilized to join cover piece 38 to molded package body 34.Alternatively, a flowable adhesive material, such as a high temperatureepoxy or other die attachment material, may be utilized to bond coverpiece 38 to molded package body 34. In this manner, air cavity 36 issealingly enclosed after device installation and electricalinterconnection. Finally, if not yet performed, leadframe 68 can besingulated or trimmed as previously-described to complete fabrication ofpackage 20.

The foregoing has thus described a method for fabricating amicroelectronic package (package 20) containing an internal shieldstructure (shield structure 58) formed as an integral part of aleadframe (leadframe 68). In further embodiments, the internal shieldstructure or structures integrated into a given internally-shieldedmicroelectronic package may be provided or produced in various othermanners. For example, the internal shield structure can be provided adiscrete-fabricated structure or insert piece, which is bonded to,mechanically joined to, or otherwise affixed to infrastructure of themicroelectronic package in some manner; e.g., in further embodiments ofpackage 20, such an inserted shield structure may be joined to leadframe68, flange frontside 42, or the underside of cover piece 38. In stillother embodiments, the internal structure may be provided as integralportion of the underside of a cover piece or other structure (e.g., awindow frame) from which the microelectronic (e.g., ACM) package isassembled. Examples of such alternative package architectures andmanufacturing approaches will now be described in conjunction with FIGS.8-11.

Further Examples of Internally-Shielded Microelectronic Packages

FIG. 8 is an isometric view of an internally-shielded ACM package 80,which is illustrated in a partially-fabricated state and depicted inaccordance with a further exemplary embodiment of the presentdisclosure. In many respects, internally-shielded ACM package 80 issimilar to ACM package 20 described above in conjunction with FIGS. 1-7,with the illustrated stage of manufacture of package 80 most closelycorresponding to that shown in FIG. 6 for package 20. Accordingly, thereference numerals introduced above have been carried over to FIG. 8,where appropriate, and portions of internally-shielded ACM package 80already discussed will not be described again to avoid redundancy. Forexample, ACM package 80 is produced utilizing a leadframe 82, which issimilar (although not identical) to leadframe 68 shown in FIGS. 4-8 andincludes a number of package leads 22, 24 26, 28, 30, 32. Also, as waspreviously the case, base flange 40 is positioned against leadframe 82and molded package body 34 is formed over and around selected portionsof base flange and leadframe 82 to arrive at the stage of manufactureshown in FIG. 8.

Once again, ACM package 80 is fabricated to include an internal shieldstructure 84. However, in the embodiment of FIG. 8, internal shieldstructure 84 is provided as a discretely-fabricate structure or insertpiece rather than as an integral portion of leadframe 82. Generally, byfurnishing internal shield structure 58 as an insert piece (rather thanas an integral portion of a leadframe) affords greater flexibility inthe design and composition of structure 58, albeit with the tradeoff ofa slight increase in manufacturing complexity. Such flexibility may beparticularly useful when internal shield structure 58 and leadframe 82are desirably fabricated from different materials. For example, in suchembodiments, leadframe 82 may be produced from a first material (e.g.,Cu) having a first electrical conductivity and a first magneticpermeability, while internal shield structure 84 is produced (at leastin principal part) from a second material (e.g., Mu metal, electricalsteel, an iron-rich alloy, or the like) having an electricallyconductivity less than and a magnetic permeability greater than thefirst material. In such embodiments, internal shield structure 84 may bepredominately composed of a such a magnetically-permeable material, byweight; and, in certain instances, may be plated with or otherwisecoated with an electrically conductive material (e.g., anickel-pallium-gold (NiPdAu) plating) for electrical shielding purposes.In other embodiments, internal shield structure 84 can be composed of acomposite material containing magnetically-permeable (e.g., Fe orferrite) particles or other filler; or any other material having arelative magnetic permeability (μr) exceeding 1000 and, more preferably,exceeding 10,000.

Internal shield structure 84 may be installed and secured within ACMpackage 80 at any stage in manufacture and can be joined to differentcomponents included within ACM package 80; e.g., shield structure 84 canbe bonded to frontside 42 of base flange 40 as a freestanding structureor, instead, bonded to the underside of a non-illustrated cover piece inembodiments. In the illustrated example, specifically, internal shieldstructure 84 is positioned and secured within internally-shielded ACMpackage 80 prior to overmolding by attachment to leadframe 68. This maybe more fully appreciated by referring to FIG. 8, which is a detailedview of one end portion of internal shield structure 84 and thesurrounding package infrastructure, which corresponds to the region ofpackage 80 identified in FIG. 7 by dashed circle 86. Here, it can beseen that the opposing end portions of internal shield structure 84terminate in enlarged retention tabs 88. A fastener opening 90, such asa countersunk bores, is provided in each retention tab 88. Fasteners 92are received through openings 90 and utilized to secure retention tabs88 and, more broadly, shield structure 84 to leadframe 82. Fasteners 92can be, for example, posts or pins integrally formed with or otherwisejoined to leadframe 82, which are received through openings 90 and thendeformed outwardly or expanded utilizing a staking operation tomechanically capture shield structure 84 against leadframe 82. Inalternative embodiments, various other joined techniques can be utilizedto attach shield structure 84 to leadframe 82 including, for example,bonding and spot welding. In addition to retention tabs 88, internalshield structure 84 includes a shield wall 94, anchor portions 96 joinedto opposing ends of shield wall 94, and flexures 98 between shield wall94 and anchor portions 96. Anchor portions 96 extend through moldedpackage body 34 to connect to retention tabs 88, as shown.

Internal shield structure 84 may be formed with a relatively largenumber of like shield structures from a sheet or strip ofmagnetically-permeable material. In this case, a forming operation maybe performed to rotate shield wall 94 into an upright orientation, withflexures 98 undergoing controlled bending to accommodate rotation ofshield wall 94 in the previous-described manner. In other embodiments,internal shield structure 84 can be fabricated in another manner therebyeliminating the need for such forming processes and the provision offlexures 98. For example, in other embodiments, internal shieldstructure 84 can be fabricated from a magnetically-permeable alloy bycasting or utilizing a three dimensional metal printing process, such asDirect Metal Laser Sintering (DMLS). Alternatively, and as indicatedabove, internal shield structure 84 can be produced by molding from acomposite material containing magnetically-permeable (e.g., Fe orferrite) particles or other filler. Various other constructions are alsopossible. For example, in another implementation, internal shieldstructure 84 may contain a core piece or portion fabricated from a firstmaterial and to which a magnetically-permeable sheet or strip is joined;e.g., by bonding or by physically clipping the magnetically-permeablestrip onto shield wall 94 of structure 84. Following attachment ofinternal shield structure 84 to leadframe 68 and formation of moldedpackage body 34, leadframe 82 may be trimmed. Trimming of leadframe 82and, specifically, severing of dam bars 72 electrically isolatesinternal shield structure 84 from package leads 22, 24, 26, 28, 30, 32.Afterwards, device attachment (e.g., bonding of devices 44, 46 shown inFIG. 3), device interconnection, and attachment of a cover piece (e.g.,cover piece 38 shown in FIGS. 1-2) may be performed to completefabrication of ACM package 80, as previously described.

In still further embodiments, the internal shield structure may beattached to or integrally formed with the underside of a cover pieceincluded in the microelectronic (e.g., ACM) package. Further emphasizingthis point, FIG. 10 is a partially exploded isometric view of amicroelectronic package 100 illustrated in accordance with anotherexemplary embodiment of the present disclosure. Microelectronic package100 is similar to package 80 (FIGS. 8-9) and package 20 (FIGS. 1-3),with like reference numerals carried forward where appropriate.Additionally, FIG. 11 further illustrates the underside of a cover piece102, which is attached to molded package body 34 of microelectronicpackage 100 to enclose air cavity 36 and devices 44, 46 containedtherein. As can be seen in FIG. 11, an internal shield structure 104 iscoupled to the underside of cover piece 102. In embodiments, internalshield structure 104 may be integrally formed with cover piece 102. Morespecifically, internal shield structure 104 may have a core portionintegrally formed with cover piece 102 by, for example, molding; and amagnetically permeable coating, paint, or plating may then be appliedover the core portion. Alternatively, internal shield structure 104 maybe separately fabricated and then adhered to the underside of coverpiece 102 in the desired position. Cover piece 102 may also includevarious other structure features, such as a lower peripheral rim or lip106, which engages an upper peripheral rim 108 of package body 34.

A bead of adhesive 110 may further be applied around lip 106 for sealingand attachment purposes.

The positioning of internal shield structure 104, as considered whencover piece 102 is installed over molded package body 34, is indicatedin FIG. 10 by dashed rectangle 112. As can be seen, when cover piece 102is properly positioned over package body 34, the lower edge of internalshield structure 104 may be matingly or conformally received within agroove, slot, or open trench 116 formed in a central portion of flangefrontside 42. If desired, a body or layer of bonding material 114 may bedispensed or otherwise provided at the juncture between the lower edgeof shield structure 104 and flange frontside 42; e.g., bonding material114 may partially fill trench 116 when provided. Bonding material 114may be provided to help secure cover piece 102 to package body 34 and tofurther help retain shield structure 104 in its desired position.Additionally or alternatively, bonding material 114 may be provided forelectrical interconnection purposes and, specifically, to electricallyjoin internal shield structure 104 to base flange 40; e.g., in anembodiment, shield structure 104 may be coupled to electrical groundthrough bonding material 114 and base flange 40. In such embodiments,bonding material 114 may be composed of a metal-filled epoxy, a sinteredmetallic material, or another electrically-conductive adhesive.

CONCLUSION

There has thus been provided embodiments of internally-shieldedmicroelectronic packages containing EM shield structures, as well asmethods for producing such microelectronic packages. Such internalshield structures favorably reduce EM cross-coupling between differentsignal paths contained in the microelectronic packages, even theassembly is operated at higher (e.g., RF) power levels and is impartedwith a relatively compact form factor. While principally described abovein the context of high power RF applications, the EM-shieldedmicroelectronic packages can be utilized in various differentapplications in which EM cross-coupling between different signal linesis problematic, whether the signal paths carry digital signals (e.g., asin the case of clock lines), analog signals, or a combination thereof.

In various embodiments, the internally-shielded microelectronic packageincludes a substrate, such as a base flange, having a frontside and alongitudinal axis. A first microelectronic device mounted to thefrontside of the substrate, while a second microelectronic devicefurther mounted to the frontside of the substrate and spaced from thefirst microelectronic device along the longitudinal axis. An internalshield structure includes or consists of a main body or shield wall,which is positioned between the first and second microelectronic devicesas taken along the longitudinal axis. The internal shield structure atleast partially composed of a magnetically-permeable material (e.g., amaterial having a relative magnetic permeability (μ_(r)) exceeding 1000and, perhaps, exceeding 10,000) decreasing EM cross-coupling between thefirst and second microelectronic devices during package operation. Insome implementations, the microelectronic package may further include afirst pair of package leads to which the first microelectronic device iselectrically coupled, as well as a second pair of package leads to whichthe second microelectronic device is electrically coupled, with thefirst pair of package leads, the second pair of package leads, and theinternal shield structure comprise singulated pieces of a leadframe. Incertain cases, the internally-shielded microelectronic package mayfurther include a package body in which the first microelectronic deviceand the second microelectronic device are contained, as well as firstand second package leads extending from a side of the package body. Insuch cases, the internal shield structure may further include a shieldextension projecting from the package body and extending between thefirst and second package leads.

In other embodiments, the internally-shielded microelectronic packageincludes a first microelectronic device (e.g., a first semiconductordie), a second microelectronic device (e.g., a second semiconductordie), and a package body (e.g., a molded package body) containing thefirst and second microelectronic devices. An internal shield structureincludes or consists of a shield wall, which is further contained withinthe package body. The shield wall is positioned between and, thus,physically partitions the first and second microelectronic devices. Theshield wall includes, in turn, (i) a magnetically-permeable layer orportion having a first magnetic permeability and a first electricalconductivity, and (ii) an electrically-conductive layer or portionbonded to the magnetically-permeable layer. The electrically-conductivelayer has a second magnetic permeability less than the first magneticpermeability and has a second electrical conductivity greater than thefirst electrical conductivity. In certain embodiments, themagnetically-permeable layer may assume the form of a singulated pieceof a leadframe over which the electrically-conductive layer isdeposited; e.g., in such embodiments, the body of leadframe may becomposed of a Mu metal, a permalloy, or another material having arelatively high magnetic permeability, with an electrically-conductivelayer (e.g., a CuNiPdAu-containing alloy) plated or otherwise depositedover portions of the leadframe forming the shield wall and, perhaps, theinternal shield structure generally. The electrical-conductive layer canalso be plated over other regions of the leadframe across whichelectrical conductivity is desired; e.g., portions of the leadframeforming package leads. In still other instances, this relationship maybe reversed such that the leadframe body is composed of anelectrically-conductive material (e.g., Cu) and a magnetically-permeablelayer is plated or otherwise deposited over those regions of theleadframe serving as the internal shield structure.

Methods for fabricating internally-shielded microelectronic packageshave further been provided. In embodiments, the method includes thesteps or processes of (i) providing a substrate having a frontside, (ii)mounting first and second microelectronic devices to the frontside ofthe substrate, and (iii) positioning a shield wall between the first andsecond microelectronic devices before or after mounting themicroelectronic devices to the frontside of the substrate. The shieldwall at least partially composed of a magnetically-permeable material(e.g., a material having a relative magnetic permeability (μ_(r))exceeding 1000 and, perhaps, exceeding 10,000), which decreases EMcross-coupling between the f microelectronic devices during packageoperation. In certain embodiments, the method may further includeattaching the substrate to a leadframe and forming (e.g., viaovermolding) a package body bonded to the leadframe. The package body isformed to contain the microelectronic devices and the shield wall; e.g.,in certain embodiments, the package body may peripherally bound orotherwise help define an air cavity in which the microelectronic devicesand the shield wall are located. An internal shield structure (in whichthe shield wall is included) may further be provided, with the internalshield structure fixedly connected to the leadframe. For example, insuch embodiments, the shield structure may be integrally formed with theleadframe (e.g., as described above in conjunction with FIGS. 4-7) orprovided as a discrete piece or insert, which is staked or otherwiseaffixed to the leadframe b(e.g., as described above in conjunction withFIGS. 8-9). In still other embodiments in which the substrate assumesthe form of a base flange serving as a ground terminal of themicroelectronic package, the method may further include the step orprocess of forming an electrical connection between the shield wall andthe base flange; e.g., by disposing an electrically-conductive adhesiveat a juncture between a lower edge of the shield wall and the frontsideof the base flange.

While at least one exemplary embodiment has been presented in theforegoing Detailed Description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing Detailed Description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set forth in the appendedclaims.

1. An internally-shielded microelectronic package, comprising: asubstrate having a frontside and a longitudinal axis; a firstmicroelectronic device mounted to the frontside of the substrate; asecond microelectronic device further mounted to the frontside of thesubstrate and spaced from the first microelectronic device along thelongitudinal axis; and an internal shield structure comprising a shieldwall positioned between the first and second microelectronic devices astaken along the longitudinal axis, the internal shield structure atleast partially composed of a magnetically-permeable material decreasingelectromagnetic cross-coupling between the first and secondmicroelectronic devices during operation of the internally-shieldedmicroelectronic package.
 2. The internally-shielded microelectronicpackage of claim 1 wherein the substrate comprises a base flangecontacted by the internal shield structure.
 3. The internally-shieldedmicroelectronic package of claim 2 wherein the internal shield structureis further composed of an electrically-conductive material coupled toelectrical ground through the base flange.
 4. The internally-shieldedmicroelectronic package of claim 1 wherein the internal shield structurecomprises: an electrical shield layer; and a magnetic shield layerhaving a magnetically permeability greater than that of the electricalshield layer and having an electrically conductivity less than that ofthe electrical shield layer.
 5. The internally-shielded microelectronicpackage of claim 4 wherein one of the magnetic shield layer and theelectrical shield layer is plated onto the other of the magnetic shiedlayer and the electrical shield layer.
 6. The internally-shieldedmicroelectronic package of claim 1 further comprising: a first pair ofpackage leads to which the first microelectronic device is electricallycoupled; and a second pair of package leads to which the secondmicroelectronic device is electrically coupled; wherein the first pairof package leads, the second pair of package leads, and the internalshield structure comprise singulated pieces of a leadframe.
 7. Theinternally-shielded microelectronic package of claim 1 wherein the firstmicroelectronic device has a first height as taken along an axisorthogonal to the frontside of the substrate, wherein the secondmicroelectronic device has a second height as taken along the axis, andwherein the internal shield structure comprises a shield wall having aheight exceeding the first and second heights.
 8. Theinternally-shielded microelectronic package of claim 1 furthercomprising: a package body; and a bond pad shelf extending around aninner periphery of the package body, the internal shield structureextending between opposing edges of the bond pad shelf.
 9. Theinternally-shielded microelectronic package of claim 8 wherein the bondpad shelf has a first width and the internal shield structure has asecond width as taken along an axis orthogonal to the longitudinal axis,the second width equal to or greater than one half the first width. 10.The internally-shielded microelectronic package of claim 1 furthercomprising: a package body at least partially defined by the substrate;and a cover piece bonded to the package body and to which the internalshield structure is attached.
 11. The internally-shieldedmicroelectronic package of claim 10 wherein at least a portion of theinternal shield structure is integrally formed with the cover piece. 12.The internally-shielded microelectronic package of claim 1 furthercomprising an open trench formed in the frontside of the substrate, theinternal shield structure having a lower edge portion received in theopen trench.
 13. The internally-shielded microelectronic package ofclaim 1 further comprising: a first lead; a first bondwire arrayelectrically interconnecting the first microelectronic device with thefirst lead; a second lead spaced from the first lead as taken thelongitudinal axis; and a second bondwire array electricallyinterconnecting the second microelectronic device with the second lead,a portion of the internal shield structure further located between firstbondwire array and the second bondwire array as taken along thelongitudinal axis.
 14. The internally-shielded microelectronic packageof claim 1 wherein the first microelectronic device comprises a firsttransistor die, wherein the second microelectronic device comprises asecond transistor die, and wherein the first and second transistor diecomprise radio frequency power amplification circuitry.
 15. Theinternally-shielded microelectronic package of claim 1 furthercomprising: a package body containing the first microelectronic deviceand the second microelectronic device; and first and second packageleads extending from a side of the package body, the first and secondpackage leads electrically coupled to the first microelectronic deviceand to the second microelectronic device, respectively; wherein theinternal shield structure further comprises a shield extensionprojecting from the package body and extending between the first andsecond package leads.
 16. The internally-shielded microelectronicpackage of claim 1, wherein the substrate forms a portion of a packagebody, and, comprises: a magnetically-permeable portion composed of themagnetically-permeable material and having a first magnetic permeabilityand a first electrical conductivity; and an electrically-conductiveportion bonded to the magnetically-permeable portion, theelectrically-conductive portion having a second magnetic permeabilityless than the first magnetic permeability and having a second electricalconductivity greater than the first electrical conductivity.
 17. Theinternally-shielded microelectronic package of claim 16 wherein themagnetically-permeable portion comprises a singulated piece of aleadframe, and wherein the electrically-conductive portion comprises anelectrically-conductive layer deposited over the singulated piece of theleadframe.
 18. A method for fabricating an internally-shieldedmicroelectronic package, the method comprising: providing a substratehaving a frontside; attaching first and second microelectronic devicesto the frontside of the substrate; and before or after attaching thefirst and second microelectronic devices to the frontside of thesubstrate, positioning a shield wall between the first and secondmicroelectronic devices; wherein the shield wall is at least partiallycomposed of a magnetically-permeable material decreasing electromagneticcross-coupling between the first and second microelectronic devicesduring operation of the internally-shielded microelectronic package. 19.The method of claim 18 further comprising: attaching the substrate to aleadframe; forming a package body bonded to the leadframe afterattaching the substrate to a leadframe, the package body containing thefirst and second microelectronic devices and the shield wall; andproviding an internal shield structure in which the shield wall isincluded, the internal shield structure fixedly connected to theleadframe.
 20. The method of claim 18 wherein the substrate comprises abase flange serving as a ground terminal of the internally-shieldedmicroelectronic package, and wherein the method further comprisesforming an electrical connection between the shield wall and the baseflange.